This invention relates to a variable capacity wobble plate compressor, and more particularly to a compressor of this kind which is adapted to compress refrigerant gas in an air conditioning system for automotive vehicles.
Already known, e.g. from Japanese Provisional Patent Publication (Kokai) No. 58-158382, which corresponds to U.S. Ser. No. 352,225 filed Feb. 25, 1982, now U.S. Pat. No. 4,428,718, is a variable capacity wobble plate compressor which employs a pressure regulating valve arranged across a communication passageway between the high pressure chamber and the crankcase with its bottom portion serving as an oil sump, wherein the pressure regulating valve is controlled to close and open the communication passageway so as to regulate the pressure within the crankcase to thereby vary the capacity of the compressor.
In compressors in general, lubrication of various sliding component parts is performed by lubricating oil entrained in compression fluid. The problem with such lubricating oil is that the oil is discharged into the refrigerating circuit from the crankcase together with the compression fluid in which it is mixed. A typical example of such phenomenon is the foaming of the oil stored in the bottom portion of the crankcase which tends to force lubricating oil at the start of the compressor, so that little or no oil is left within the crankcase.
In order to overcome such disadvantage, the following measures have conventionally been employed for instance:
(1) Return lubricating oil, which has flowed out of the oil sump in the crankcase, circulated in the refrigerating circuit and entered a piston cylinder during a suction stroke by means of blow-by during the piston compression stroke while entrained in the blow-by gas.
(2) Provide a passageway permanently communicating between the high pressure chamber and the crankcase so that lubricating oil separated from discharge compression fluid is returned to the crankcase through the passageway.
However, according to the former measure, the return rate of lubricating oil is too small to obtain a sufficient oil storage amount in the oil sump of the crankcase, while the latter measure suffers from degradation of the compression efficiency because part of the compression fluid once discharged into the high pressure chamber always flows to the crankcase through the aforementioned passageway during operation of the compressor.
A further measure would be to return to the crankcase lubricating oil separated from compression fluid in a zone under a lower pressure such as the suction pressure chamber. However, in a wobble plate compressor of the type concerned, generally the pressure within the crankcase is higher by 0.1-1.5 kg/cm.sup.2 than that in the lower pressure zone, so there is no tendency for causing flow of lubricating oil from the lower pressure zone to the crankcase.